ISO vs ASME Drawing Standards — What's the Difference?

When you commission engineering drawings, one of the first questions is which standard to follow — ISO or ASME. The answer depends on where your product is being manufactured and who your client is.

What is ISO?

ISO (International Organization for Standardization) drawing standards are used predominantly in Europe, Australia, the Middle East, and most of Asia. Key standards include ISO 128 (drawing presentation), ISO 1101 (GD&T), and ISO 2768 (general tolerances). ISO drawings use first-angle projection.

What is ASME?

ASME (American Society of Mechanical Engineers) standards are the dominant standard in the USA and Canada. The core standard is ASME Y14.5 for GD&T. ASME drawings use third-angle projection. Many international clients in oil & gas and pressure vessel work also specify ASME.

Key Differences

• ✓Projection angle — ISO uses first-angle, ASME uses third-angle
• ✓GD&T symbols — largely aligned but with some differences in application
• ✓Title block format — different layouts and mandatory fields
• ✓Surface finish symbols — different notation systems
• ✓Welding symbols — slight notation differences

Which Should You Use?

Follow your client's requirement. If you are manufacturing in Australia for a US client — use ASME. If you are manufacturing in Europe for a local client — use ISO. When in doubt, specify it explicitly on your drawing. At TDM, we work to both standards and will always confirm which applies before starting your project.